About 80 percent of men diagnosed with prostate cancer survive for at least 10 years after diagnosis. That is good news, but it also means it is important for doctors to look at the long-term effects of cancer treatments. External-beam radiation therapy, a non-invasive procedure in which a high-intensity beam of radiation hits the cancerous area, killing both cancer and normal cells, is one of the most popular treatments for prostate cancer. However, since other areas of the pelvis are also hit by radiation, it could increase the risk of other types of cancer. Researchers from the University of Minnesota and the University of North Carolina looked to see if there was a link between prostate radiation therapy and rectal cancer.

What the researchers wanted to know: Does radiation therapy for prostate cancer increase a man's risk of rectal cancer?

What they did: The researchers looked at data from nearly 86,000 men between the ages of 18 and 80 who were diagnosed with prostate cancer between 1973 and 1994. They split the men up by the type of treatment they had, prostatectomy or radiation (with or without surgery). Men with other types of treatment, such as the removal of a testicle, were excluded from this study. Because radiation usually takes between five and 15 years to cause a tumor, the researchers analyzed the percentage of men in each treatment group who developed colon or rectal cancer at least five years after receiving treatment for prostate cancer.

What they found: Men who received radiation therapy were 70 percent more likely than those who received only surgery to develop rectal cancer, but no more likely to develop cancer in other parts of their colon. The rectum is usually the part of the body most directly hit by radiation during the treatment of prostate cancer, so the researchers say it makes sense that the area would be most at risk for the development of cancer years later.

What it means to you: The researchers compared the increased risk due to radiation therapy with the risk a man has if there is a history of rectal cancer in his family. They say that this study should not turn patients away from radiation therapy for prostate cancer but that a man who has been treated this way may want to be screened regularly for rectal cancer.

Caveats: Since 1995, the time when the most recent patients in this study were treated, external beam radiation technology has improved so that doctors are able to better focus just on the area of the prostate where cancer is located. Because of these improvements, the risk of a later cancer in men undergoing radiation therapy today may not be as high as it is for men who underwent radiation a decade or two ago.

Find out more: The Prostate Cancer Foundation has a wealth of information about prostate cancer, including different treatment options and how to choose among them.

Radiation is only one of the risk factors for rectal cancer. Read about risks for both colon and rectal cancer on the National Cancer Institute's website.

Read the article: Baxter, N. N. et al. "Increased Risk of Rectal Cancer After Prostate Radiation: A Population-Based Study." Gastroenterology. April 2005, Vol. 128, No. 3, pp. 819–824.